The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Plastic containers, such as polyethylene terephthalate (“PET”), have become commonplace for the packaging of liquid products, such as fruit juices and liquid sports drinks, which must be filled into a container while the liquid is hot to provide for adequate and proper sterilization. Because these plastic containers are normally filled with a hot liquid, the product that occupies the container is commonly referred to as a “hot-fill product” or “hot-fill liquid” and the container is commonly referred to as a “hot-fill container.” During filling of the container, the product is typically dispensed into the container at a temperature of at least 180 degrees F. (82.2 degrees C.). Immediately after filling, the container is sealed or capped, such as with a threaded cap, and as the product cools to room temperature, such as 72 degrees F. (22.2 degrees C.), a negative internal pressure or vacuum forms within the sealed container. Although PET containers that are hot-filled have been in use for quite some time, such containers are not without their share of limitations.
One limitation of PET containers that receive a hot-filled product is that during cooling of the liquid product, the containers may undergo an amount of physical distortion that causes the container to become aesthetically unpleasing, difficult to hold with a human hand, makes the container structurally undesirable, and susceptible to falling over or becoming non-stackable. More specifically, a vacuum or negative internal pressure caused by a cooling and contracting internal liquid may cause the container body or sidewalls to deform in unacceptable ways to account for the pressure differential between the volume inside of the closed container and the space outside, or atmosphere surrounding, the container. To compensate or permit such deformation to be controlled, vacuum panels may be incorporated into the container as portions of the sidewall. Typically, more than one vacuum panel may be employed to control the inwardly moving sidewall of the container during product cooling and container volume displacement. Such vacuum panels may generally be aesthetically unpleasing, limit container sidewall design, restrict convenient placement of sidewall hand grips, and limit container shape and size.
Another limitation of current PET containers that receive a hot-filled product is that they are generally limited to a prescribed wall thickness to limit deformation in particular areas; that is, a wall thickness that can not be thinner or lower than a prescribed value. Such thicknesses are generally necessary to prevent sidewall deformation in prescribed sidewall areas and promote use of the vacuum panels resident in the container sidewall.
Another limitation of current PET containers that employ vacuum panels is that container sidewall areas that do not employ such vacuum panels may be required to be designed with a specific geometry to account for internal vacuum pressures to ensure structural integrity of the sidewall in order to maintain the desired overall container geometry.
Another limitation of plastic containers, such as hot-fill containers, is that deformation in a top location of the container is normally limited since containers are top-loaded and sufficient strength in the top area is necessary to ensure container integrity. Such a limitation means that vacuum accommodating vacuum panels must be located in another area of the container, such as a mid or lower sidewall. Another limitation is that typically when containers undergo deformation in a sidewall, top loading of the container may no longer be possible, thus limiting packaging options for stacking.
Another limitation of hot-filled plastic containers is that such containers may be susceptible to buckling during storage or transit. Typically, to facilitate storage and shipping of PET containers, they are packed in a case arrangement and then the cases are stacked case upon case. While stacked, each container is subject to buckling and compression upon itself due to direct vertical loading. Such loading may result in container deformation or container rupture, both of which are potentially permanent, which may then render the container and internal product as unsellable or unusable.
Yet another limitation with hot-filled containers lies in preserving the body strength of the container during the cooling process. One way to achieve container body strength is to place a multitude of vertical or horizontal ribs in the container to increase the moment of inertia in the body wall in select places. However, such multitude of ribs increases the amount of plastic material that must be used and thus contributes to the overall weight, size and cost of the container. When container walls and vacuum panels are necessary to be a prescribed thickness, limiting container weight presents a challenge. Accordingly, costs associated with container material and costs associated with shipping the container materials, both before and after container manufacture, may be higher than if a lesser amount of container material was able to be used per container, while maintaining container volume.
Finally, current containers do not permit for container shapes other than the standard, largely cylindrical, elongated shape. By permitting other container shapes, beyond what a vacuum panel permits, additional and greater product volume displacements may be afforded to hot-fill containers yet maintaining the integrity of container vertical strength and providing an aesthetically pleasing container.